Indoor air within and around enclosed environments, such as buildings, vehicles and structures, is affected by a plurality of contaminants. Among these contaminants, often with the highest concentration, is carbon dioxide (CO2). There are other contaminants which may appear in relatively lower concentrations yet are no less important to monitor and/or reduce. A class of such contaminants is a group of species of organic vapors, broadly referred to as Volatile Organic Compounds (VOC). Contaminate gases (e.g., CO2) and VOCs, and corresponding vapors thereof, may collectively be referred to as a “gas(es)”. The sources of these contaminants include, inter alia, the human occupants themselves—from respiration and perspiration to clothing and cosmetics—as well as building materials, equipment, food and consumer products, cleaning materials, office supplies or any other materials which emit VOCs. Other classes of contaminants are inorganic compounds and microorganisms such as bacteria, viruses, mold, fungi and airborne particles. Additional gaseous contaminants may be sulfur oxides, nitrous oxides, radon, or carbon monoxide.
Heating, Ventilation and Air-Conditioning (“HVAC”) is used in virtually every modern building. One of the goals of HVAC systems is to provide a comfortable and healthy environment for the enclosed environment occupants, in terms of temperature, humidity, composition and quality of air.
There are various HVAC system configurations known in the art.
A central HVAC system generally includes one or more central air handling units, which is operative to adjust the temperature or humidity of air received therein. The air exiting the central air handling unit is supplied to the enclosed environment via an air circulation system. In the central HVAC system the air circulation system is formed with ducts directing the supply air from the central air handling unit to various locations in the enclosed environment. In enclosed environments, such as buildings, comprising a plurality of indoor spaces, such as rooms, a network of ducts direct the supply air into each room. The air exiting the enclosed environment is returned to the central air handling unit.
As noted above, in order to maintain good air quality, not all the air is returned. Some of the air is exhausted out of the enclosed environment and is replaced by an intake of fresh air from the outside. This is sometimes referred to as “fresh air”, “makeup air” or ventilation. Such replacement of the air dilutes the contaminants within the indoor air and helps maintain good air quality in the enclosed environment.
However, there are a number of drawbacks to fresh air ventilation, including the energy required to condition the outdoor air, as well as the potential introduction of pollutants and contaminants from the outside into the enclosed environment. One possible solution to these drawbacks is to selectively remove the contaminants from indoor air, and certain schemes have been proposed for this purpose in conjunction with central HVAC systems. For example, a system for removing the contaminants from indoor air in a central HVAC system is disclosed in applicant's U.S. Pat. No. 8,157,892, which is incorporated herein by reference in its entirety.
Selective contaminant removal from the central HVAC system is performed by directing the return air flowing within the ducts to a contaminant remover system and thereafter introducing the now treated return air back into the ducts. Generally the return air is directed to the contaminant remover system from the ducts directing the return air from the enclosed environment to the central air handling unit.
An alternative HVAC system is a distributed air circulation system. This distributed system generally conveys chilled (or heated) fluid to the plurality of indoor spaces, such as rooms, within the enclosed environment, where local air circulation units, such as fan-coil units circulate the indoor air. The fan-coil unit generally comprises a coil chilled (or heated) by the fluid. The coil is provided for adjusting the temperature or humidity of the circulated air and a fan or blower is provided for circulating the indoor air.
The chilled or heated fluid can originate from a centralized chilling or heating system shared by a plurality of fan-coil units, or from a single dedicated heat pump unit. As known in the art, the fluid can be supplied by a Variable Refrigerant Flow (VRF) system, a Fixed Refrigerant Flow system, or by a direct expansion (DX) system. In other distributed air circulation systems the fluid may be water.
The fan coil unit is placed within a room or space, typically within a recess in the ceiling or walls of the room. The fan coil unit may be placed in a plenum adjacent to the room. The circulating air flows from the air circulation unit into the room substantially without reliance on ducts (i.e. a ductless supply) and back from the room or space towards the air.
In order to maintain good air quality, some of the air is released out of the enclosed environment and is replaced by an intake of fresh outdoor air. Such replacement of the air dilutes the contaminants within the indoor air and helps maintain good air quality in the enclosed environment. The outdoor air generally enters the enclosed environment via a duct.
In some distributed air circulation systems, a central fresh air pre-conditioning unit initially cools (or heats) the outdoor air prior to entering ducts leading to the various rooms or fan-coil units inside the building. In other distributed air circulation systems the outdoor air directly enters the room, plenum or the air circulation unit wherein the outdoor air temperature is adjusted.
The energy required to condition the outdoor air, as well as the potential introduction of pollutants and contaminants from the outdoor into the enclosed environment are significant deficiencies of the outside air ventilation in these systems.
Embodiments of the present disclosure are directed to remedy these deficiencies.